Electric steam generation

ABSTRACT

A steam generator e.g. for a hand-held portable appliance such as a domestic iron or steam cleaner comprises a water inlet, a boiler, a valve for controlling the entry of water into the boiler and means for delivering a surge of water to the boiler when the valve is opened. Also disclosed is an adaptor for supplying electrical power to a mobile electrical appliance. The adaptor is operable in a corded mode when secured to the appliance for supplying electrical power and water while the appliance is being used; or a cordless mode when secured to a base unit such that electrical and water connection can be made by placing the appliance on or against the base unit; and broken by lifting or moving the appliance away from the base unit.

This application is entitled to the benefit of, and incorporates byreference essential subject matter disclosed in PCT Application No.PCT/GB2010/000206 filed on Feb. 4, 2010, which claims priority to GreatBritain Application No. 0901855.7 filed Feb. 5, 2009. It is also relatedto PCT Application No. PCT/GB2010/000212 filed on Feb. 4, 2010.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to the electric generation of steam for use indomestic irons, steam cleaners, wallpaper strippers and other hand-heldsteam generating appliances and to various related components.

2. Background Information

Domestic steam irons have been around for a long time. They comprise asole plate which is flat and intended to contact the item to be ironedand which is normally heated by means of a sheathed electricalresistance heater mounted to or embedded in the upper side of the soleplate. Traditionally, such irons which are designed to produce steam inorder to improve ironing have a semi-closed cavity formed on the upperface of the sole plate and into which water is dripped from an on-boardreservoir to produce steam which is then allowed to escape onto theclothes by means of a series of apertures formed in the sole plate.These are commonly known as vented steam irons. They are relativelysimple and inexpensive to implement which has made them very popular.However, the steam produced is at very low pressure (essentially ambientpressure) and cannot be produced very quickly, making it relativelyineffective.

At the other end of the market, are professional or semi-professionalsteam ironing systems in which high pressure steam (e.g. of the order of3 to 5 bar) is continuously produced in a static base stationincorporating a large water reservoir which can then be fed, on demand,to the user's hand-held unit by means of an umbilical cord. These arecommonly known as pressurized steam generator irons. They deliver a veryhigh performance but are very expensive and tend to account thereforeonly for a very small proportion of the market.

More recently there have been proposals, some of which have beencommercialized, which seek to bridge the gap between the two extremesoutlined above, although these have tended to carry their own drawbacks.For example, it has been proposed to provide a boiler in a base unit,separate from the iron, which is fed by pumping water into it from areservoir in the base station. The main disadvantage with thesearrangements, commonly known as instantaneous steam generator irons, isthat there is in fact a significant time lag (of the order of 10seconds) between the user pressing a button to demand steam and thesteam actually being produced and conveyed to the iron. Thissignificantly limits user acceptance, even though higher steam flowrates than vented steam irons can be achieved when the steam iseventually delivered.

It is an aim of the present invention to provide an improved arrangementfor generating steam on demand which can be used in steam irons, andalso in other devices employing steam, such as steam cleaners, wallpaperstrippers, other hand-held steam generating appliances etc.

SUMMARY OF THE DISCLOSURE

When viewed from a first aspect the invention provides a steam generatorcomprising a water inlet, a boiler, a valve for controlling the entry ofwater into the boiler and means for delivering a surge of water to theboiler when the valve is opened.

Thus it will be seen by those skilled in the art that in accordance withthe invention steam can be produced “on demand” by opening the valve toadmit water into the boiler, whilst the inherent time lag is reduced byproviding an initial surge of water into the boiler. The surge of waterallows the boiler to be filled more rapidly than if it were simplysupplied by water at the steady-state flow rate at which it can producesteam. This minimizes the delay in the user having the steam available.The surge volume, which can be considered to be the total volume ofwater supplied over and above what would have been supplied at thesteady-state flow rate, will typically need to be less than the volumeof the boiler. The surge volume might be such that when added to the“normal” flow the boiler is filled to its design capacity. In someembodiments the surge volume is at least half the volume of the boiler.

In preferred embodiments the boiler is provided in a portable appliancesuch as a steam iron, steam cleaner, wallpaper stripper or otherhand-held steam generating appliance. This also helps in significantlyreducing the time lag between a user demanding steam and the steam beingdelivered, as compared to an arrangement with the boiler in a base unit.As well as being beneficial in minimizing the delay in delivering steam,it obviates the need to provide tubes and connectors which are capableof withstanding pressurized steam between the base unit and the mobileunit.

Although the boiler will typically be thermostatically controlled, it ispreferably arranged such that it is allowed to reach a higher operatingtemperature when there is no water flow (i.e. when the valve is closed)than when the valve is opened and water is flowing. This means that theboiler can store additional thermal energy in its thermal mass, furtherreducing the time to produce the first shot of steam after the valve isopened because the surge of water can then be heated more rapidly.

Many ways can be envisaged of providing the initial surge of cold waterin accordance with the invention set out above. For example, a pumpmight be provided for pumping water into the boiler which is configuredso that when the valve opens, the pump delivers a higher flow rate thanits steady-state flow rate. However, this is presently considered arelatively complex and expensive option.

Another possibility would be to provide an arrangement in which thesurge of water is provided manually by a user. Conveniently, forexample, this could be provided by a suitable mechanism arranged todeliver the extra water, which mechanism was coupled to a button orlever that is operated by the user in order to demand the supply ofsteam. In just one example of such an arrangement, a lever coupled tothe steam knob or the like might be used to expel water from anadditional store, or other means could be used.

It should be noted that in accordance with the invention set out above,the surge of water could be provided independently of the ordinary flowof water into the boiler when the valve is opened, e.g. by means of aseparate inlet, but preferably it comprises a temporarily enhanced flowrate after the valve is opened.

In a preferred set of embodiments, water is stored in anelastically-charged store upstream of the valve. The water in theelastically-charged store can therefore provide the additional flow toprovide the surge when the valve is first opened. Theelastically-charged store could be provided in a number of ways. In onepossibility envisaged by the applicant it simply comprises anelastically expandable tube for supplying water to the boiler. Indeed,depending upon the material used for the tube and the pressure at whichwater is supplied by means of it, some swelling of the tube may beinevitable. However, the applicant has recognized in the context of thedesirable features set out above, that this can be positively exploitedin order to deliver some or all of the surge of water in accordance withthe invention.

Additionally or alternatively, a discrete elastically-charged storecould be provided. In one set of embodiments, the store comprises areservoir acted upon by a resiliently mounted piston. In another set ofembodiments, the store has one or more expandable walls. The wallsthemselves could be elastically expandable and/or could expand into anelastically compressible surrounding medium. In a set of embodiments,the elastically-charged store comprises a bladder, preferably anelastically expandable bladder, which is arranged within an appliance toexpand into a space within the appliance. This is particularlybeneficial as the bladder can expand into an irregularly shaped spacethus making it easier to accommodate within an appliance withoutcompromising the external design.

The water for supplying the boiler may be provided in a number of ways.In a set of preferred embodiments the boiler is provided in a portableappliance also including a reservoir. Water could be supplied from thereservoir to the boiler in a number of different ways. For example, itmight simply be disposed in an upper part of the appliance (with respectto the orientation in which the appliance is normally meant to be used)such that the water is supplied under hydrostatic force. Anotheralternative would be to provide a pump. In a set of embodiments, thereservoir is pressurized. This could for example be achieved by means ofa compressed air chamber or the reservoir could be elastically charged.

The on-board reservoir discussed above could be integrated with thepreviously described elastically-charged water store for providing theinitial surge of water to the boiler where such a store is provided. Inanother set of embodiments however the reservoir is separate.

As in the case of the elastically charged “surge” store discussed above,where a separate on-board reservoir is provided it could be acted uponby a resiliently mounted piston. In another set of embodiments, thereservoir has one or more expandable walls. The walls themselves couldbe elastically expandable and/or could expand into an elasticallycompressible surrounding medium. In a set of embodiments, the reservoircomprises a bladder, e.g. an expandable bladder arranged such thatpressure is applied to the water therein when expanded. This might bebeneficial as the bladder can expand into an irregularly shaped spacethus making it easier to accommodate within an appliance withoutcompromising the external design. Indeed, since the reservoir will needto have a greater capacity than the “surge” store, the advantageobtainable from the collapsible bladder embodiments are potentiallygreater since the ability to be able to use irregularly shaped spaces inthe appliance will be even more useful.

In some of the embodiments where the boiler is provided in a portableappliance together with a reservoir, the appliance could comprise meansfor a user to refill the reservoir. In another set of embodiments a baseunit comprising a base reservoir is provided, the portable appliancebeing a corresponding mobile unit. This might allow the mobile unit tobe operated cordlessly, by refilling the on-board reservoir when themobile unit is replaced on the base unit. Another (not mutuallyexclusive) possibility is for the mobile unit to be operable either in acordless mode as set out above or in a corded mode in which water issupplied directly from the base reservoir.

In a cordless arrangement the capacity of the on-board reservoir, i.e.that provided on the mobile unit, can be designed to give a certainperiod of use off the base before it must be replenished. Conveniently,this time is related to the time taken for the boiler and/or the soleplate in the case of an iron to fall below a certain minimum temperaturefor useful operation. Preferably the capacity of the reservoir issufficient to provide the water to generate steam for more than 10seconds, preferably more than 15 seconds, preferably more than 20seconds. In some embodiments enough water is stored for 30 seconds ormore of steam.

In other embodiments comprising a mobile unit and a base unit, themobile unit remains attached to the base unit by means of a cord so thatthe base unit supplies water to the boiler in the mobile unit. Typicallysuch a cord would also supply electrical power to the appliance. In suchembodiments an on-board reservoir to allow for cordless use is notrequired. An elastically-charged store may nonetheless be provided toprovide the surge. In alternative embodiments employing a fixedelectrical cord, no base unit is provided and a reservoir is provided onthe appliance which can be refilled by a user. Again anelastically-charged store may also be provided to provide the surge.

In embodiments comprising a base unit with a base reservoir, the baseunit preferably comprises a pump for pumping water from the basereservoir to the mobile unit. In embodiments with no base reservoir apump is preferably provided on the appliance for pumping water from thereservoir to the boiler.

In one set of embodiments the pump (wherever it is provided) is arrangedto operate continuously whilst the appliance is switched on. Thisensures that pressure is maintained for minimizing the amount of timeeither to refill the elastically-charged surge store (where provided),to refill the on-board reservoir—where a base reservoir and on-boardreservoir are provided, or simply to deliver water to the boiler. Abypass valve—e.g. to deliver water back to the reservoir—may be providedto prevent the pump stalling or drawing excessive current when deliveryof water is not required.

In some embodiments, particularly those having a fixed electrical cordor operating in corded mode, there may be provided means to delayoperation of the pump until the boiler has reached a predeterminedoperating temperature. A temperature sensitive control means may bearranged to provide an electrical connection to the pump only when it isdetected that the operating temperature has been reached. Alternativelya timer could be programmed to delay the operation of the pump untilsuch time that the boiler is expected to have heated up. It is preferredthat the pump and the electric heating means of the boiler are connectedelectrically in parallel so that they may be controlled by a commonon/off switch. This allows for simple “one button” operation of theappliance, while also ensuring that the boiler is hot enough when wateris pumped into it that steam generation starts rapidly. Advantageouslythe start-up time may be reduced.

When viewed from a further aspect the invention provides a cordlesselectrical mobile appliance comprising a water reservoir for storingwater under pressure, the water reservoir comprising an expandablebladder arranged such that pressure is applied to the water therein whenexpanded.

Any of the essential or preferred features of the first aspect of theinvention set out above may be applied to this invention. Thus in oneset of embodiments the appliance comprises a boiler and so could be asteam iron, steam cleaner, wallpaper stripper or any other hand-heldsteam-generating appliance. Furthermore it is preferable for a base unitto be provided including a further reservoir for refilling said waterreservoir.

In accordance with all previous aspects and embodiments of theinvention, preferably the boiler comprises a water inlet, an electricheater, a steam outlet and an evaporation space bounded by at least onesurface in thermal contact with the heater, wherein the evaporationspace is configured to present an expanding cross-sectional area in adirection away from the water inlet. This corresponds to an increasinginternal volume in the evaporation space and a corresponding increase insurface area during the advancement and a corresponding rise intemperature of the water and steam. In accordance with sucharrangements, the evaporation space can start off relatively small togive good intimate contact between the water and the heated surface(s)of the evaporation space to give efficient evaporation of the water,whilst at the same time allowing the steam so generated to expand intothe increasing volume as it flows away from the water inlet e.g. to anoutlet.

Such an arrangement is novel and inventive in its own right and thuswhen viewed from a further aspect the invention provides a boiler for asteam generator appliance comprising a water inlet, an electric heaterand an evaporation space bounded by at least one surface in good thermalcontact with the heater, wherein said evaporation space is arranged suchthat it expands in cross-section in a direction away from water inlet.

In some embodiments in accordance with such arrangements the evaporationspace is very shallow to maximize the surface area over which the wateris spread to enhance the efficiency of steam generation. In an exemplaryset of embodiments, the height of the evaporation space is narrow enoughto prevent drops from forming—e.g. less than 3 mm. In some embodimentsthe evaporation space has a constant, preferably shallow height. In somepossible implementations of the boiler, the evaporation space is formedbetween two similarly shaped surfaces in close proximity to one another.The separation of the surfaces provides the height of the evaporationspace and thus in a set of preferred embodiments they are separated by agap of less than 3 mm.

Clearly when the height of the evaporation space is constant, theclaimed expanding cross-section is provided by an increasing width togive the recited increase in the cross-sectional area of the evaporationspace in a direction away from the water inlet. In some exampleembodiments, the evaporation surface is convex, concave or conical.Other substantially two or three dimensional forms such as fans, deltas,hemispheres, parabolas, prisms, pyramids and other suitable forms can beemployed to provide the required increasing volume and surface area. Ofcourse, other, more complex, shapes could be used to give the sameeffect, both internally to enhance surface area and so evaporationefficiency and externally to minimize the space required for the boilerin the appliance Equally however the evaporation space could simplycomprise an open chamber—in other words it is not essential for it to benarrow.

The heated surface bounding the evaporation space (hereinafter referredto as “the evaporation surface”) is preferably non-planar. Thisfacilitates maximizing the surface area available in a given volumeoccupied by the boiler within the appliance. In a set of preferredembodiments, the surface area of the evaporation surface (measured priorto the application of any surface enhancing coating) is more than 1.5times the maximum planar projection of the surface (i.e. the footprint),more preferably greater than 1.75 times, more preferably greater thantwice.

The evaporation space could be empty until it is filled withwater/steam, although in one set of embodiments a lattice or meshstructure is provided. In some circumstances this can enhance theefficiency of steam generation by increasing the effective area which isheated and can also help to reduce the Leidenfrost effect (whereby smalldroplets of water are separated by an insulating layer of steam whenwater comes into contact with a very hot surface). In an exemplary setof embodiments, a woven metal mesh is located within the evaporationspace. The mesh structure could be lightly compressed against theevaporation surface, e.g. by being trapped between two confrontingsurfaces as previously mentioned so that the extremities of the mesh'smajor surfaces, those created by the alternating under and overrelationship of the mesh's woven elements, contact the evaporationsurface and the confronting surface in a corresponding alternatingarrangement. Filling the evaporation space with a lattice or mesh canhelp to restrict the flow of water particles, but allow the freerpassage of steam, so increasing the evaporation efficiency of theboiler. In one set of embodiments a woven stainless steel mesh or meshesis employed which is advantageously corrosion resistant. However otherconfigurations can provide a similar advantageous effect, e.g. anexpanded mesh, a perforated material, a fibrous material etc.

Additionally, or alternatively, the evaporation surface could beprovided with a texture, structure or coating to increase its surfacearea at a microscopic level and/or to mitigate the Leidenfrost effect.For example the surface could comprise steps, tessellations or texturecreating a myriad of channels or small structures for increased surfacearea and turbulence to flow within the evaporation space.

Preferably the evaporation surface is hydrophilic, at least at itsnormal operating temperature. In an exemplary set of embodiments thenormal operating temperature is greater than 160° C. This might be anatural characteristic of the material used for the evaporation surface,it might be achieved or enhanced by a suitable surface treatment and/orit might be achieved or enhanced by a suitable heat resistant coatingmaterial. Where the evaporation surface is made hydrophilic by a surfacetreatment or coating the treated or coated surface should be hydrophilicat a temperature at which the Leidenfrost effect would otherwise occuron the untreated or uncoated surface.

In a set of embodiments the evaporation surface is coated with a coatingcomprising zeolite particulates. Preferably said zeolite particles areof a nano and micro scale. In a set of embodiments the coating comprisesaluminosilicate particles. In an exemplary set of embodiments theparticles have the CAS number 1318-02-01 or similar. Preferably such acoating comprises a binder which acts as a carrier medium to facilitatethe application as a thin film between 3 microns to 100 microns inthickness but more preferably between 3 microns and 50 microns inthickness. The binder is preferably formulated not to saturate thestructure of the zeolite particles and to facilitate a functional filmlayer with micro-porous properties, improving surface wetting andexhibiting minimal surface tension in contact with water.

Prior to drying or curing to form the functional coating, the zeoliteparticulates are held in suspension within the binder. Upon hardening toform the functional coating the zeolite particles are thereafterencapsulated or partially encapsulated by the binder to create a nanoand or micro scale structured open cell syntactic matrix where thezeolite particulates act as scaffolds with interlinking nano and ormicro scale voids creating a partially open and partially closed cellstructure. Prior to the application of the functional coating, theinternal surfaces of the boiler may be prepared via surface rougheningand degreasing, where the surface is abraded and a defined textureresults to assist in mechanical bonding of the functional coating to theprepared surface but also to further impart a texture. Such a texturecan influence the heat transfer surface of the functional coating. Thepreferred surface roughening method would be high pressure grit blastingor blasting with any other suitable substrate to create the preferredfinish. However other suitable methods may be employed.

The use of a zeolite coating having the optional features set out aboveon the evaporation surfaces of a boiler or other liquid heater,particularly one for a compact portable electrical appliance such as asteam iron, is novel and inventive in its own right. When viewed from afurther aspect therefore the invention extends to the use of a coatingcomprising zeolite particulates on a surface heated to heat a liquid incontact therewith to enhance the transfer of heat between the surfaceand the liquid. The invention also extends to a heater or boiler havingsuch a coating applied thereto.

In a set of embodiments, at least part of the evaporation space isconfigured so as to present an interrupted flow path. Advantageously,such a structure could be provided at least in a portion nearest to anexit of the evaporation space, i.e. furthest from the water inlet. Sucharrangements have been found to enhance the evaporation of water whichhas not been evaporated and also to physically separate unevaporateddroplets of water from the steam. The Applicant has found that a similareffect can be found by throttling or otherwise restricting the flow ofsteam.

The evaporation space may of course have more than one evaporationsurface. This might be the case as a result of the distribution of theheating element, the provision of multiple heating elements, or simplyby the close thermal connection between a surface which is directlyheated and another surface.

In a set of preferred embodiments the boiler is configured to producesuper-heated steam. In some preferred embodiments the boiler has atemperature of between 100 and 500° C., more preferably between 105 and380° C. Preferably the internal steam pressure generated within theboiler should not be greater than that of the water pressure enteringit, or water will be prevented from entering the device, resulting in asubsequent drop in steam flow rate and unwanted fluctuation in steamoutput.

Steam may simply be allowed to leave the boiler once it has passedthrough the evaporation space. However, in a set of preferredembodiments the boiler comprises means for collecting the steam. Thisallows it, for example, to be channeled into one or more pipes fordelivering it to the steam outlet(s) of an appliance on which the boileris provided. The means for collecting steam may comprise means fortrapping unevaporated droplets of water. For example this might be aprotruding outlet tube encouraging steam channeled by the walls of thechamber to undergo a change of direction leading to expulsion ofentrained droplets.

In a set of embodiments the boiler is divided into the evaporation spaceand a steam collection space. In a set of embodiments the boiler isdivided by an intermediate member provided in the chamber of the boiler.Preferably the intermediate member provides one of the surfaces definingthe evaporation space.

A boiler in accordance with the aspect of the invention set out abovemay usefully be used for the continuous generation of steam. However, itis particularly beneficial for appliances where steam is required “ondemand” since the features described above, at least in their preferredembodiments, allow the very rapid production of steam from when waterfirst enters the water inlet as compared, for example, with a moretraditional boiler in which a heating element is used to heat a body ofwater. An important factor in achieving this effect is to supply waterto the boiler under pressure and thus a particularly preferred set ofembodiments has a boiler of the kind described above, or indeed onewhich only has some of the features set out, which might include thefeature of expanding cross-sectional area, in an appliance comprisingmeans for supplying pressurized water to the water inlet of the boiler.As previously mentioned, such an appliance could, for example comprisean electric iron, a steam cleaner, wallpaper stripper or any otherhand-held steam generating appliance. The means for pressurizing watercould be any of those discussed above or indeed any other. The pressureof the water supply is preferably greater than 0.5 bar, e.g. more than 1bar and might be up to 3 bar or more.

Where the boiler is to be used to produce steam “on demand” it isbeneficial, in order to minimize the initial delay between filling itwith water and producing steam, that when it does not contain water, itis allowed to increase in temperature and therefore store thermal energywhich can be used to heat the initial charge of water to boiling asrapidly as possible. In a set of preferred embodiments, the useableenergy which the boiler is adapted to store, that is the amount of heatenergy available to generate steam, is more than 20 kilojoules, morepreferably greater than 35 kilojoules and more preferably greater than50 kilojoules.

As will be apparent from the discussion above, in many embodiments ofthe invention there is a mobile appliance and a base unit. For manyelectrical appliances, it is convenient for a mobile unit to have acordless electrical connection to a base unit. This might, for example,be because the mobile unit includes a battery which only needs periodicrecharging when placed on the base unit, or it could be that, forexample in the case of a kettle or coffee maker, electrical power isonly needed for a short time and the cordless connection allows theappliance to be moved to where it is needed. However the invention alsoextends to appliances with a fixed electrical cord.

In the case of irons, although there are many cordless irons availableand these have obvious convenience advantages, there is a perceptionacross a significant part of the market that cordless irons,particularly cordless steam irons, have a substantially inferiorperformance as compared to corded versions since by definition energycannot be supplied while the iron is being used. The Applicant hasrecognized that there are advantages and disadvantages both ways. It hastherefore devised an arrangement which seeks to achieve some of theadvantages of both arrangements. In accordance with some embodiments ofthe invention therefore there is provided an adaptor for supplyingelectrical power to the mobile appliance, said adaptor being operable ina first, corded mode in which it is secured to the appliance to permitelectrical power to be supplied while the appliance is being used; or ina second, cordless mode in which electrical connection between theadaptor and the appliance can be made by placing the appliance on oragainst the adaptor; and broken by lifting or moving the appliance awayfrom the adaptor.

Thus it will be seen that in accordance with these embodiments of theinvention, a mobile appliance may be operated either in a corded or in acordless mode depending upon the requirements of the user. For examplein the context of an electric iron, if a user wished to carry out aseries of light ironing tasks, perhaps without the use of steam, he orshe could conveniently use the iron in the cordless mode and replace iton the adaptor to reheat it between garments. Alternatively if a heavyironing task arose, perhaps requiring a lot of steam, the user canattach the adaptor to the iron and enjoy the benefits of the ability tosupply electrical power while the iron is actually being used.

The adaptor could be designed to be placed directly on a surface whennot secured to the appliance, but in a set of preferred embodiments itis designed to be secured instead to a base unit. This is novel andinventive in its own right and thus when viewed from a further aspectthe invention provides an adaptor for supplying electrical power to amobile electrical appliance, said adaptor being operable in a first,corded mode in which it is secured to the appliance to permit electricalpower to be supplied while the appliance is being used; or in a second,cordless mode in which it is secured to a base unit such that electricalconnection between the adaptor and the appliance can be made by placingthe appliance on or against the base unit; and broken by lifting ormoving the appliance away from the base unit.

The adaptor could be connectable directly to a suitable power outlet toprovide electrical power, but preferably it is connected to the baseunit, with the base unit in turn being connected to the power outlet.

As will be apparent from the foregoing, one of the advantageous possibleimplementations of the invention is in the context of a hand-held steamappliance. Accordingly, in a preferred set of embodiments the adaptoralso comprises means for supplying water to the appliance. Again, thiscould conceivably come from a separate water connection directly to theadaptor but preferably it comprises a water reservoir in the base unit.Thus when viewed from another aspect the invention provides an adaptorfor supplying electrical power to a mobile electrical appliance, saidadaptor being operable in a first, corded mode in which it is secured tothe appliance to permit electrical power and water to be supplied whilethe appliance is being used; or in a second, cordless mode in which itis secured to a base unit such that electrical and water connectionbetween the adaptor and the appliance can be made by placing theappliance on or against the base unit; and broken by lifting or movingthe appliance away from the base unit.

Providing a water supply can allow operation in a cordless mode, whenthe adaptor is not attached, whereby a reservoir of water in the iron isused and replenished when the appliance is replaced on the adaptor; or acorded mode whereby water and electricity can be supplied to permitlonger and/or higher performance use. Preferably the means for supplyingwater from the adaptor to the appliance comprises valve means on eitherside of the connection to prevent leakage either from the adaptor orfrom the appliance when the two are not connected, during the process ofconnection, or when connected.

The appliance and base unit should be designed so that they do notinadvertently disconnect from one another. When only an electricalconnection is being made, it is relatively easy to achieve this simplyby means of the weight of the appliance, which would typically be muchgreater than the spring force necessary to maintain a good electricalconnection between the electrical contacts. However, where a waterconnection is also provided, particularly where the water supply is atsignificant pressure, the weight of the appliance alone may not besufficient to ensure that a firm connection is maintained since as wellas the electrical contact spring force, the force required to hold therespective valves open and the force exerted by the water pressure willtend to act to separate the connectors.

In some possible embodiments of the invention therefore the base unitand/or the appliance are configured to prevent unwanted disconnectiontherebetween. In some embodiments, such configuration can be provided bymeans which secure the appliance to the base unit. Indeed, this couldsimply be the same means by which the adaptor can be secured to theappliance for use in corded mode. However, this is considered to berelatively inconvenient for a user as it requires positive disconnectionof a clip or other fastening means before the appliance can be lifted ormoved from the base station which negates some of the convenienceadvantages associated with a cordless appliance.

In a set of embodiments the base unit and appliance comprise means forpreventing separation in a direction substantially parallel to the axisof the connection, but which permit removal of the appliance in adirection non-parallel to said axis. In such embodiments theconfiguration of the base and appliance prevent disconnection under theforce of the pressurized water supply tending to separate the connectorsand/or the contact force of the electrical connector, whilst stillallowing the user to remove the appliance from the base simply pickingit up in an appropriate direction. One possible way of implementing thiswould be to provide a recess on the base unit into which the appliancecould be seated by a tilting or rotating action with the distal wall ofthe recess, or indeed any other mechanical arrangement, preventingmovement along the connector axis, i.e. tangential to the tilting actionrequired to place or remove the appliance Another example would be ahook or ridge on one of the appliance or the base unit cooperating witha corresponding feature on the other.

Such an arrangement is novel and inventive in its own right and thuswhen viewed from a further aspect the invention provides a cordlesselectrical steam-generating system comprising a base unit and a cordlessappliance wherein said base unit and appliance comprise mutuallycooperating connection means supplying a pressurised fluid from the baseunit to the appliance, said base unit and appliance further comprisingmeans for preventing mutual separation in a direction parallel to theaxis of the connection, but which permits removal of the appliance in adirection non-parallel to said axis.

As mentioned above, this arrangement is particularly beneficial wherethere is a relatively high force tending to separate the connectors,e.g. where the connectors include a pressurized water connector. In anexemplary set of embodiments of this aspect of the invention and theassociated embodiments of previous aspects, the force tending toseparate the connectors is greater than a quarter of the weight of theappliance. In such applications, it could be inadvisable to rely on theweight of the appliance alone to provide the connector closure forcesince the relatively significant opposing force can make a secureconnection difficult and can make the connection unstable to beinggently knocked or rocked.

Since in accordance with the arrangements set out above it is no longernecessary to rely on the weight of the appliance to provide the closureforce on the connectors, the system designer is given greater freedom asto the orientation on which the appliance rests on the base unit. Thus,rather than requiring the cordless water and possibly electricalconnectors to be provided on a face of the appliance on which theappliance is adapted to stand, they could be applied by a differentsurface. To give an example in the context of an electric iron, thecordless connectors might be provided on the back end of the iron onwhich the iron is stood when it is being rested during use, but whenplaced on the base, the iron could be placed at an angle nearer to thehorizontal or indeed fully horizontal. Accordingly, in a set ofembodiments a cordless base unit is provided having electrical power andwater connections on a surface having an angle of less than 45° to thevertical.

Where a cordless arrangement is provided for both electrical power andwater, completely independent connectors could be provided. However,this could make it more difficult to mate the appliance with the baseunit as it might require simultaneous alignment between the two separateconnectors. In preferred embodiments, the power and water connectionsare provided with a mutual alignment of mating parts, often referred toin the art as a common coning arrangement. In other words, there is asingle guidance alignment system to control the direction of approach ofthe appliance to the base unit during engagement or disengagement. In aset of preferred embodiments the connections are arranged such thatafter physical contact has been made between one pair of connectors andthey are subsequently brought towards their full alignment axis,physical contact is made between the other pair of connectors. Havingsequential contact like this is beneficial where one pair of connectorshave a greater tolerance to the initial angle when contact is first madethan the other pair of connectors. For example the tolerance to initialangle, often known as the coning angle, tends to be greater for theelectrical connectors than for the water connectors.

The water and electrical connectors could be arranged side by side.However in some embodiments they are arranged one above the other; thatis one at a greater height than the other, when the iron or otherappliance is on its base unit. This is beneficial as it limits thedegree of alignment which it is necessary for a user to carry out, giventhat the base unit gives alignment in a vertical plane.

In one set of embodiments, one half of each connector could be providedin a concave formation on one of the appliance on the base part with theother halves of the connectors being provided in a corresponding convexformation on the other of the base unit and the appliance.

In some sets of embodiments of various aspects of the invention, a baseunit is used to provide a pressurized water supply to a cordlessappliance unit when the latter is placed onto the base. In some suchembodiments, the base water supply is continuously pressurized sincethis allows a pressurized reservoir in the appliance to be recharged inaccordance with the preferred embodiments. As alluded to earlier, evenin an arrangement where the base and appliance are configured to preventthe pressure of the water separating the connectors when the applianceis fully engaged on the base, the presence of the water pressure and theforce required to hold the respective valves open could nonetheless makeit more difficult for a user to bring the connectors together. These areboth in addition to the force exerted by the spring contacts in theelectrical connector.

In one set of embodiments, the base unit is provided with means forreducing the pressure of a pressurized water supply while a user isconnecting, and optionally disconnecting, the cordless appliance to/fromthe base unit. There are of course many ways in which this could bedone. For example, manual intervention by a user, e.g. to press abutton, could be used. Preferably however the base unit is arranged todetect when the cordless appliance is brought into engagement with it.

There are any manner of ways in which this can be done using optical,magnetic, capacitance sensors, etc. but preferably a simple micro-switchis arranged to be operated as the appliance is brought into engagement.This could be an electrical micro-switch to reduce the pressure e.g. byreducing the speed of or switching off a pump, or a direct mechanicalarrangement e.g. closing a valve or throttle to limit or stop waterflow.

In accordance with all aspects and embodiments of the invention wherepressurized water is either supplied to or stored within a mobile unit,the pressure of the water is preferably at least 0.5 bar preferably atleast 1 bar and in some cases is greater than 3 bar.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain preferred embodiments of the invention will now be described, byway of example only, with reference to the accompanying drawings inwhich:

FIG. 1 is a perspective view of an iron in accordance with an embodimentof the invention;

FIG. 2 is a view of an adaptor for supplying electrical power and waterto the iron shown in FIG. 1;

FIG. 3 is a cut-away view showing the internal components of the ironwith the adaptor fitted;

FIG. 4 is a view similar to FIG. 3 with some of the internal componentsremoved for clarity;

FIG. 5 is a view of the internal components making up the water andsteam system;

FIG. 6 is an enlarged cross-sectional view of the two pressureaccumulators;

FIG. 7 is an enlarged view of the compact steam generator module;

FIG. 8 is an exploded view of the steam generator with the outer coverremoved;

FIG. 9 is a sectional view through the steam generator;

FIG. 10 is another sectional view through the steam generator;

FIG. 11 is a perspective view of the iron described with reference toFIGS. 1 to 10, operating in a corded mode, and a base station;

FIG. 12 is a view of the base configured for use of the iron in acordless mode;

FIG. 13 is a view of the iron seated on the base;

FIGS. 14 a-e show schematically various alternative embodiments ofeither or both of the pressure accumulators;

FIG. 15 is a perspective view of another embodiment of the invention;

FIGS. 16 and 17 are views from the side and rear respectively of theappliance of FIG. 15 with the outer housing removed;

FIG. 18 is a sectional view through the pressure accumulator;

FIG. 19 is a view of the boiler; and

FIG. 20 is an exploded view of the boiler.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an external view of a steam iron 1 which embodies severalaspects of the invention. In FIG. 1 can be seen the main body 2, anelectrically heated sole plate 4 and a handle 6. A temperature selectorknob 8 is provided on the body 2 beneath the handle 6. A further knob 10is provided on the front of the handle 6 to allow a user to control theamount of steam supplied by the iron (alternatively it could simplyallow steam to be switched on or off). At the rear of the iron is acordless electrical connector 24—here the male part of the Applicant'sP75 cordless electrical connector set but of course any other suitableconnector could be used—and a water connector 26.

FIG. 2 shows an adaptor unit 12 for connection to the rear of the ironfor supplying the iron with electrical power and water. The adaptorcomprises an outer body 14. Projecting from one face of the body 14 isthe female part 16 the Applicant's P75 cordless connector set. Above theelectrical connector 16 is the water connector 18 which comprises avalve 20. An umbilical cord 22 connects the adaptor 12 to a base unit(not shown) and carries inside it separately insulated electrical wiresand a tube for carrying water. These are connected to the electricalconnector 16 and the water connector 18 respectively.

FIGS. 3 and 4 show cut-away views of the iron with the adaptor 12connected to it. Thus, at the rear of the iron the electrical connectors16, 24 are mating as are the water connectors 18, 26. The waterconnector parts 18, 26 are configured so that when they are sealinglyconnected to one another, pressure is applied to the valve 20 and to acorresponding valve (not shown) in the iron-side connector part 26 toallow water to flow. The valves on each respective water connector 18,26 prevent the leakage of water when the adaptor 12 is separated fromthe iron.

On the inner face of the iron's sole plate 4 is an element block 28inside which is provided a resistance heating element for heating thesole plate 4 as is conventional. The sole plate element is connected tothe electrical power inlet 24 by means of a thermostat arrangement 30which can be seen more clearly in FIG. 4 but which is in good thermalcontact with the sole plate element. The temperature control knob 8 isconnected to the thermostat arrangement 30 in order to switch power onand off and to set the thermostat to give the desired temperature rangeof the sole plate 4. The boiler module 52 is also visible.

The water and steam system inside the iron will now be described withreference to FIG. 5 in which the other parts of the iron have beenremoved for clarity. A short flexible tube 32 connects the water inletconnector 26 to a T-piece connector 34, the stem of which is connectedto a pressure accumulator 36, which in use forms an on-board waterreservoir as will be explained in greater detail further below. Afurther short tube 38 joins the T-piece connector 34 to a second T-piececonnector 40 on a second pressure accumulator 42, which in use acts as asurge water store as will be explained in more detail further below.

FIG. 6 shows a sectional view of the two pressure accumulators 36, 42 inmore detail. As may be seen from this Figure, inside each pressureaccumulator 36, 42 is a sprung piston 37, 43 respectively. These pistons37, 43 apply pressure to water which is stored inside the respectiveaccumulator. The pressure applied is dependent upon the spring force ofthe corresponding spring. In this embodiment, the spring force of thepiston 43 in the surge accumulator 42 is greater than that of the piston37 in the on-board reservoir accumulator 36. This means that once thesurge accumulator 42 has emptied during the initial period of watersupply, it will not be refilled by the on-board reservoir accumulator36.

A longer piece of flexible tubing 44 connects the T-piece connector 40on the surge accumulator 42 to a variable valve 46 which is operated bythe user-operable steam knob 10. Alternatively a simple on-off valvecould be used. Downstream of the valve 46 is a further tube 48 whichconnects at its other end to the inlet 50 of the boiler module 52. Theboiler module 52 is described below in greater detail with reference toFIGS. 7 to 10. The steam outlet 54 from the boiler module is connectedto a further tube 56 which conveys the steam exiting the boiler module52 into a plenum in the element block 28 formed on the upper side of thesole plate 4 (refer to FIG. 3) and out from there through a plurality ofapertures in the sole plate.

The novel boiler module 52 will now be described in greater detail withreference to FIGS. 7 to 10. FIG. 7 shows the external appearance of theboiler module 52. The boiler 52 is largely covered by a heat-resistantcover 58 which is e.g. made of one or more layers of mica, but can bemade of any suitable substance. In the lower right hand region (whenviewed from FIG. 7) of the module there can be seen the water inlet 50and the end of a sheathed electrical resistance heating element 60. Aprojecting metal connector 62 (known in the art as a cold tail) isprovided to enable electrical connection to the element 60. A similarcold tail 64 is provided at the other end of the element which isvisible on the left hand side of FIG. 7. A high temperature regulator 66is provided against a flange 68 (see FIG. 8) on the lower body member 70of the boiler.

The steam outlet 54 is visible in the top, left hand part of FIG. 7.

With particular reference now to FIG. 8, it can be seen that the mainsection of the boiler is made up of four main parts: the lower bodymember 70, a corresponding upper body member 72 and an intermediateconical member 74 which may all be made of non-ferrous die-cast metal orother suitable material; and a conical mesh layer 76, e.g. of stainlesssteel.

When assembled, the upper and lower body members 70, 72 are clampedtogether by suitable means and this retains the intermediate conicalmember 74 and mesh cone 76 between them. A suitably heat-resistant sealis provided between the upper and lower body members 72, 70, althoughthis has been omitted for clarity.

It may be seen that inside, the lower body member 70 defines a conicalchamber 78 which receives the intermediate conical member 74. The innerwall of this chamber 78 is formed with a series of concentric annularsteps, the purpose of which will be explained later. The conical member74 is spaced from the wall of the chamber 78 by a constant amount acrossits surface to form a narrow evaporation space. The evaporation space isfilled by the mesh 76 which is thick enough to touch the surfaces onboth sides of the narrow gap.

FIG. 9 shows a cross-section through the assembled module 52. ThisFigure shows that the lower body member 70 has much thicker walls thanthe upper body member 72 since they accommodate an embedded heatingelement 60. This is cast into the lower body member during manufacture,although is omitted from FIG. 9 so that only the passage 80 it forms isvisible. The embedding of the heating element 60 in the wall of thelower body member 70 can be seen in FIG. 10. The element isapproximately helical so that it wraps around the conical cavity formedby the lower body member 70. This ensures an even heat distributionacross the lower, tapering wall of the chamber 78.

At the lowest point of the steam chamber 78 is the opening 82 of anotherpassageway through the walls of the lower body member 70 which fluidlycommunicates with the water inlet 50. At the top of the chamber 78 thereis a steam outlet formed by a short section of tube 84 which projectsdownwardly into the chamber 78 and is in fluid communication with anarrow passageway 86 through the upper body member 72 and whichcommunicates with the steam outlet 54.

As can be seen from FIGS. 8, 9 and 10, the intermediate conical member74 comprises a solid lower portion 88 and has a series of apertures 90around its upper portion. The mesh cone has been omitted from thisFigure for clarity. It should be appreciated that neither the mesh conenor the intermediate conical member is essential.

The internal heat transfer surfaces—that is the walls of the chamber 78and the intermediate conical member 74—are coated with a functional heatresilient surface coating that enhances the transfer of heat into thewater. The coating improves the speed of heat absorbed by the waterparticularly at operating temperatures above 160° C. and below 380° C.The functional coating could instead be selectively applied just to theinterior of the evaporation space between the lower, tapering part ofthe chamber wall 78 and the solid part 88 of the intermediate member.The design of the chamber facilitates such simple selective applicationprior to assembly. The coating can be applied in a single coat. Toensure its durability it may however be necessary subsequently to cureit at an elevated temperature. The method of application need not becomplicated and can be accomplished without sophisticated equipment—e.g.via spray, brush, roller or any other suitable method. However othermethods can be employed such as electrolytic, electrostatic, plasma,thermal spray, vacuum deposition, spin coated, sol gel process,evaporation and others.

The functional coating provides a hydrophilic surface and substantiallyincreases the available heat transfer surface area of the evaporationspace by giving the coated surfaces thereof a microstructure. Amicro-surface and partially sub-surface structure is imparted by thecoating as it creates a surface matrix and micro-textured surface.Additionally the coating is thermally shock resilient, adheres stronglyto the internal surfaces and preferably inhibits corrosion.

It will be seen that the internal configuration of the boiler has heattransfer surfaces that are configured to operate at different scalesthrough use e.g. of the functional coating which operates to improvethermal transfer efficiencies at dimensions between the nano and microscales. The surface to which the coating is applied is configured toimpart a texture to the coating operating between a micro and macroscales. The stepped surface structure on the other hand operates toenhance heat transfer at a macro scale. Therefore the evaporation spaceoperates as a complex heat transfer surface/matrix with additionalcomplex heat transfer surface/matrix interactions at the micro and nanoscale provided by the functional coating. The stepped structure can alsoassist adhesion of the coating.

The various internal zones, cavities and openings of the boiler arearranged to create predetermined varying resistance to the internal flowof water/steam and also provide for a preferential direction of flow,wherein generally the zones are configured to provide a sequentialincrease in volume corresponding to the temperature of the fluid and itsproperties. Hence there are reducing obstructions and resistance to flowwithin the chamber as fluid progresses through it to the exit. Theconfiguration is such that the internal steam pressure generated withinthe boiler device is not greater than that of the water pressureentering the device. This avoids water being prevented from entering thedevice, resulting in a subsequent drop in steam flow rate and unwantedfluctuation in steam output.

FIG. 11 shows an iron 1 and corresponding base station 91 which areconfigured for use in a corded mode. Most of the volume of the base unit91 is taken up by an internal water reservoir which may be filled at aninlet spout 92. A water outlet pipe extends into the water reservoir andis terminated by a sodium, potassium or hydrogen form demineralizingfilter. The outlet pipe is connected to an electrically operated pump(not shown) which can pump water from the reservoir along a pipe in theumbilical cord 22 to the water outlet 18 of the adaptor 12 (see FIG. 2).The arrangement includes a pressure relief valve which can open into thewater reservoir either above or below the water level. This prevents adangerous build-up in pressure if there should be a blockage in any partof the system. If the pump is run continuously it also prevents stallingof the pump which would overheat it and reduce its reliability. Thefilter is provided between the reservoir and the pump but this is notessential. The recirculation of water inherent in the use of such avalve is also beneficial in improving filtration of the water.

On the top of the base unit is a stand for the iron which comprises agently inclined and curved base portion 106 and an upstand portion 108at right angles to the base portion 106. In use the base portion 106faces the sole plate of the iron and the back of the iron rests againstthe upstand portion 108. The upstand portion 108 is shaped to allow itsnugly to receive the adaptor 12. On the back of the upstand is auser-operable knob 94 which can advance or retract a locking pin 96 forlocking the adaptor 12 to the upstand 108 when the iron is being used incordless mode as will be explained below with reference to FIG. 12.

At the other end of the base unit 91 there is a rotatable clip 98 havinga C-shaped cross section. As will be explained later with reference toFIG. 13, this receives the tip of the iron's sole plate 4. A little waybeneath this, protruding from the base portion 106 is a microswitch 110which can detect when the iron has been placed on the stand. Of courseany other contact or non-contact sensor arrangement could be employedinstead.

Although not visible in FIG. 11, an electrical flex is also provided forconnecting the base unit to a mains power outlet. This provides powerfor the pump and also provides the electrical power supply to theadaptor 12 via the umbilical cord 22.

In FIG. 11 the iron is being used in a corded configuration. In thisconfiguration, the adaptor 12 is secured to the back of the iron 1 sothat water and electricity can be supplied from the base unit 91 whilethe iron is being used.

In FIG. 12, the adaptor 12 is instead secured to the upstand portion 108of the base using the locking pin 96 to allow the iron to be used in acordless mode. In this mode, water and electricity are only supplied tothe iron when it is placed on the base unit 91.

FIG. 13 shows the iron 1 seated on the base. Here it can be seen that asthe tip of the sole plate 4 has been received in the rotatable clip 98,it causes the clip to rotate and lock it against axial movement awayfrom the adaptor 12 secured to the base unit upstand 108 containing thecordless connectors 18, 24. This prevents separation of the cordlessconnectors on the iron 1 and adaptor respectively under the separationforce provided by the water pressure from the pump, the valve pressureand the electrical contact force. The C-section clip 98 preventsmovement of the iron 1 relative to the upstand portion 108 in adirection parallel to the plane of the sole plate 4, i.e. in a directionparallel to the axes of the water and electrical cordless connectors.This therefore prevents the tendency of these connectors to separate.However, placement and removal of the iron can be easily achieved bytilting the iron 1 out of the clip 98 to remove it and pivoting it intothe clip 98 to replace it. Of course, many other configurations could beused to give this effect.

FIGS. 14 a to e show, schematically, further possible embodiments of oneor both of the pressure accumulators provided in the iron (see FIG. 6for reference). FIGS. 14 a and 14 b show a pressure accumulator 116which has a flexible internal membrane 118 which divides the internalspace in the accumulator between a water receiving space 120 and acompressible medium 122, such as an elastomeric material with lowcompression set. This means that as water fills the space 120, themedium 122 is compressed but in turn applies a reactionary pressure tothe water to pressurize it.

FIG. 14 c shows a variant of this which illustrates that the walls ofthe accumulator 116′ need not be regular in shape and can therefore bedesigned to fit into an irregular space inside an appliance, therebymaking maximum use of the space available. FIGS. 14 d and 14 e show asimilar arrangement in which a bladder 124 can expand into thecompressible medium 122 as it is filled with water. The bladder 124might itself be elastically expandable to enhance the pressure on thewater when it is filled.

Operation of the iron will now be described with reference to FIGS. 1 to12.

Operation in cordless mode will be described first. With reference toFIG. 12, the adaptor 12 is secured to the upstand 108 of the base unitby means of the locking pin 96 (not visible). To commence operation, theiron 1 is placed on the base unit so that the electrical power and watercordless connectors 16, 18 respectively of the adaptor engage thecorresponding connector parts 24, 26 of the iron. In this embodimentwhen the iron is placed on the stand, its presence is sensed by themicroswitch 110 which switches on the pump to start pumping water intothe iron. Alternatively the pump can run continuously (in which case themicroswitch could be omitted. The water is pumped through the water tubein the umbilical cord 22, through the opened valves of the cordlesswater connector 18, 26 and so into the water system inside the iron.Since the user-operated variable valve 46 should be closed whilst theiron is on the base, the water pressure developed by the pump fills theon-board reservoir accumulator 36 and the surge accumulator 42 againstthe force exerted by the respective sprung pistons 37, 43. Once theaccumulators 36, 42 and various pipes 32, 38, 44 are filled with water,the system is fully pressurized and the flow of water from the tank 92in the base stops. If a pressure relief valve is provided this will thenact to divert the water to recirculate within the reservoir.

While the iron 1 is on the base 91, electrical power is supplied via theumbilical cord and cordless connector parts 16, 24 to heat the soleplate element (not shown). This heating is regulated by the thermostat30 depending upon the setting of the temperature control knob 8, as iswell known in the art. Independently of the heating of the sole plateelement, electrical power is also supplied to the sheathed resistanceheating element 60 which is embedded in the lower body member 70 of theboiler. This is controlled by a separate high temperature regulator 66which allows the boiler to reach a much higher temperature e.g. between160° C. and 380° C.

Although not shown, one or more indicator lights or other foam ofindication might be provided to a user to indicate that the water systemhas charged, the sole plate had reached the set temperature and/or theboiler had reached its predetermined temperature. The user can then liftor move the iron away from the cordless base thereby breaking theelectrical and water connections between them. The valve 20 in thecordless connector 18 on the adaptor 12 which remains on the base unitprevents the pressurized water in the umbilical cord from leaking out. Asimilar valve in the iron-side connector 26 prevents leakage from thepressurized system in the iron. Lifting or moving the iron away from thebase also causes the microswitch 110 to open again and thereby switchoff the pump unless it is configured to run continuously.

The significant thermal mass of the sole plate 4 and its element meansthat the temperature of the sole plate 4 remains sufficiently high foreffective ironing to be carried out for a reasonable time. If the usershould require steam during use of the iron, he or she simply needs tooperate the knob 10 to open the valve 46 which allows water to flow intothe boiler 52 as will be described below.

When the valve 46 is first opened, there will be a surge of water underpressure primarily from the surge accumulator 42. This initial surge ofwater rapidly fills the boiler 52 to allow steam to be generated veryquickly. This is enhanced by the high thermal capacity of the boiler,particularly the lower body portion 70 which allows a significant amountof thermal energy to be stored as a result of the high temperature whichthe regulator 66 allows it to reach. As a result of this surge, theboiler is filled nearly to its capacity and this, with the high initialtemperature of the lower body portion, produces a ‘whoosh’ of steam at agreater rate than the steady-state steam production rate.

Operation of the boiler module 52 will now be described in greaterdetail with reference to FIGS. 8 to 10. Water first enters the boiler bymeans of the inlet 50. The water passes through an internal conduit (notshown) in the lower body portion of the boiler 70. As the water passesthrough this conduit, it is preheated so that when it enters the boilingchamber its temperature is raised significantly above ambient (but belowboiling) The water enters the conical boiling chamber 78 by means of anopening 82 at its apex. The water is forced under pressure, providedinitially by the surge accumulator 42 and then by the on-board reservoiraccumulator 36. As the water is pressurized, it is forced into thenarrow gap between the stepped wall of the chamber 78 and the solidcentral portion 88 of the intermediate member 74. This provides anextremely efficient ratio of surface area to volume which allows arelatively large quantity of water to be evaporated into steam from arelatively small boiler volume. The shape of the evaporation space whichis defined between the conical wall of the chamber 78 and thecorresponding conical member 88 means that the cross sectional area ofthe evaporation space increases in a direction away from the inlet 82 asthe water travels up the cone. This increasing volume allows forexpansion of the steam created during the evaporation process and solimits the tendency for a build up in pressure to reduce the inflow rateof water. The very narrow evaporation space, the stepped form of thechamber wall and the zeolite coating which is applied to the chamberwall and the intermediate member 74 together act to mitigate theLeidenfrost effect such that this effect does not have a significantimpact on the rate of evaporation.

The steam which is produced escapes from the evaporation space betweenthe lower part of the chamber 78 and the intermediate member 74 throughthe series of apertures 90 formed in the latter. The pressure of thissteam forces it out of the outlet pipe 84 in the top of the chamber 78.Since the outlet pipe 84 projects slightly into the chamber 78 thishelps to trap any small remaining droplets of water entrained in thesteam so that these fall onto the central portion 88 of the intermediatemember 74 and are evaporated. The steam exiting the steam chamber 78 issuperheated. The steam passes through the internal conduit 86 to thesteam outlet 54 and from there into the steam pipe 56 to be ventedthrough suitable apertures in the sole plate (not shown). Clearly, theuser can regulate the rate at which steam is generated by operating theknob 10 to alter the degree of opening of the variable valve 46 andthereby alter the flow rate of water into the boiler 52.

As mentioned above, the surge accumulator 42 provides an initial surgeof water to fill the evaporation space within the boiler 52 as quicklyas possible to enable steam to be produced very quickly (in a matter ofless than a few seconds) after the user opens the valve 46 by means ofthe knob 10. Thereafter, water is supplied by the on-board reservoiraccumulator 36. This will continue to supply water under pressure untilthe on-board reservoir is no longer elastically charged. In one example,the capacity of this on-board reservoir 36 is designed to give steam atmaximum rate (i.e. with the valve 46 fully open) for approximately 30seconds. Of course, the thermal energy which can be stored in the boileris also a relevant factor as this must be sufficient to evaporate all ofthe water stored in the accumulators 36, 42. Since the spring force ofthe piston 43 in the surge accumulator 42 is higher than the springforce of the corresponding piston 37 in the on-board reservoiraccumulator 36, once the surge accumulator 42 has been emptied, it willnot be refilled by the on-board reservoir accumulator 36.

Once the user has used up all the steam or the sole plate temperaturehas dropped too far, the iron may simply be replaced on the base unit 91in order to replenish the accumulators 36, 42 and reheat the sole plateelement and the boiler element 60 to permit the next cycle of use.

Cordless use is clearly convenient, particularly where a relativelylight ironing task is being completed or where there is a relativelylower requirement for steam. However, in some circumstances it is moreconvenient for a user to be able to continue ironing, and in particularusing steam, without having continually to replace the iron on thestand. In order to meet this objective, the adaptor 12 may simply bereleased from the upstand 108 of the base unit using the locking pinrelease knob 94 and instead clipped to the back of the iron as is shownin FIGS. 3, 4 and 11. In this mode, the on-board reservoir accumulator36 is not required and it simply remains partly or fully charged. Amicroswitch in the adaptor (not shown) causes the pump in the base unitto run continuously so that the system can be maintained at thenecessary pressure. The surge accumulator 42 still performs an importantrole in providing an additional flow of water when the valve 46 isopened to minimize the delay in production of steam. Since there is acontinuous electrical and water connection, steam can be producedcontinuously should the user so wish. Similarly the sole platetemperature can be maintained within the range set by the temperatureregulator knob 8.

Thus it will be seen by those skilled in the art that the embodiment ofvarious aspects of the invention described above provides an extremelyeffective and versatile steam iron which offers the performance of ahigh steam pressure but which can be produced at a significantly lowercost than traditional pressurized steam generator ironing systems.Moreover, the flexibility to change between corded and cordless modedepending upon the task at hand is particularly advantageous.

A further embodiment of the invention will now be described withreference to FIGS. 15 to 20. FIG. 15 shows a portable, hand-held steamcleaner. This comprises an outer casing 130 which defines a handle 132and has a tapering section 134 which terminates in a nozzle 136. At thetop of the cleaner is a large user actuation lever 138, a water tankfiller plug 140 and a steam pressure adjustment screw 142. On the sideof the housing 130 is a water level indicator 143.

FIGS. 16 and 17 show views from the side and rear of the apparatusrespectively with the outer housing 130 removed. From these figures, itmay be seen that a large proportion of the internal volume of theapparatus is taken up by a water tank 144 which is filled by removingthe filling cap 140. A generally vertical transparent pipe 145 allowsthe level of water in the tank to be viewed through the level gauge 143in the housing.

The rear of the water tank 144 defines a recess which accommodates apump 146 that is connected to the outlet of the water tank by a pipe148. The other side of the pump 146 is connected, by means of a pipe 150to the inlet of a pressure accumulator 152. This is shown in more detailin FIG. 18.

Referring to FIG. 18, the front face of the pressure accumulator 152comprises two nozzles 154, 156 for entry and exit of water respectivelywhich are ridged to receive the ends of respective pipes 150, 162.Although not shown, one-way valves may be provided to permit the flow ofwater only in the specified direction. The body of the accumulator 152defines an internal space together with a generally planar piston memberand diaphragm assembly 158 which is urged towards the front of theaccumulator by a coil spring 160. FIG. 18 shows the piston member 158 inits foremost position. As in previous embodiments, this arrangement issuch as to allow the storage of water inside the accumulator 152 underpressure generated by the spring 160.

Returning to FIGS. 16 and 17, the outlet of the accumulator 152 isconnected by means of a pipe 162 to a pressure regulator 164 which iscontrolled by the pressure regulating screw 142 shown in FIG. 15. Theother side of the pressure regulator 164 is connected by means of afurther pipe 166 to a user-operated valve 168 connected to the actuationlever 138. The other side of the user operator valve 168 is connected bymeans of a pipe 170 to the inlet 172 of the boiler arrangement 174. Theboiler arrangement is shown in greater detail with reference to FIGS. 19and 20.

The boiler 174 comprises a cast aluminum main body 176 which has aconical interior chamber 178 with a finely ridged surface encircled byan embedded sheathed heating element 180 as in previous embodiments. Theinterior surface of the chamber is treated or coated to render ithydrophilic thereby reducing or avoiding the Leidenfrost effect. Anintermediate conical member 182 is received in the main chamber 178thereby forming a narrow evaporation space between them. However, it hasbeen found that such an intermediate member can be omitted whilst stillachieving satisfactory performance. A cover member 184 is provided,secured to the lower main body member 176 in order to close the chamber178 in a pressure-tight manner. A centrally disposed outlet connectingto an outlet pipe 186 is provided to allow steam to exit the chamber.

As FIG. 19 shows, the boiler 174 is provided with a temperatureregulator 188 in good thermal contact with the outer surface of the mainbody member 176. The regulator 188 acts to maintain the temperature ofthe boiler within a desired range of. A further temperature regulator(not shown) is also provided and forms part of a thermally sensitivecontrol for the electrical supply to the pump 26. This furthertemperature regulator has normally-open contacts which are not closeduntil its preset temperature is reached. These contacts are connectedelectrically in series with the pump 146.

Also provided in a suitably arranged recess in the aluminum body 176, isa thermal fuse 190 which can operate to permanently disconnectelectrical power to the heating element 180 in the event of seriousoverheating—e.g. if the temperature regulator 188 should fail.

It may be seen from FIG. 16, the steam outlet 186 is connected to thenozzle of the appliance 136 by a suitably heat resistant pipe 192.

Operation of this embodiment will now be described. Before switching theappliance on, the user removes the filler plug 140 and fills the watertank 144 with water until it reaches the “max” level indicated by thegauge 143. The filler cap 140 is then replaced and the appliance may beswitched on. As will become apparent, however, an advantage of thedesign of this appliance (which advantage may be shared with many otherembodiments of the invention) is that since the water tank 144 is notpressurized and contains only cold water, a pressure cap is not requiredand furthermore there is no risk of scalding if the cap is removedimmediately after operation or even inadvertently left off.

When the appliance is switched on, the heating element 180 is energizedto heat the boiler 174. When the boiler reaches a predetermined minimumoperating temperature, for example 120-160° C., the normally-opencontacts of one of the regulators are closed, thereby switching on thepump 146. This delay can help to ensure that not too much water entersthe boiler until it is at its operating temperature which helps toensure that there are no unevaporated water droplets in the dischargedsteam.

The other regulator 188 operates to maintain the temperature of theboiler within a predetermined range by switching the element 180 offwhen a maximum operating temperature is reached—typically greater than180° C.—and back on when the boiler has cooled to a lower thresholdtemperature. The heating element 180 can continue to cycle in thismanner indefinitely. The temperature range maintained is higher than thereset temperature of the normally-open regulator described above so thatthe pump runs continuously after the delay when the appliance isinitially switched on.

Once the pump 146 is switched on, it pumps water from the water tank 144to the accumulator 152 by means of the respective pipes 148 and 150.Since at this point the user-operated valve 168 is closed, the waterpressure provided by the pump 146 works to drive down the accumulatorpiston 158 against the force of the spring 160, thereby storing waterunder pressure inside the accumulator 152. When the accumulator 152 isfull, the pump 146 continues to run. Water may be diverted by a divertervalve (not shown) back into the tank 144. In other embodiments the pumpcould be arranged to shut off automatically.

When a user requires a shot of steam, he or she simply depresses theuser actuation lever 138 which opens the corresponding valve 168. Thisimmediately allows water to enter the boiler 174 by means of the tube170 and inlet 172. While the accumulator 152 empties, the pressureprovided by the spring 160 provides an initial surge of water into theboiler, over and above the rate at which water is supplied by the pump.This has the result of giving a very rapid shot of steam through theoutlet nozzle 136. If the user continues to keep the actuation lever 138depressed, the continuously operating pump 146 will continue to deliverwater into the boiler 174, thereby producing steam for as long asrequired by the user (or until the water tank 144 is emptied). Thepressure provided by the pump 146 is matched to the maximum rate atwhich the boiler 174 can produce steam, although the pressure regulator164 may be adjusted by means of the adjustment screw 142 in order toreduce the rate at which steam is ejected through the nozzle by reducingthe pressure of the water entering the boiler 174.

Once the user lets go of the actuation lever 138, the valve 168 isclosed and the pump 146 will then once again cause the accumulator 152to be filled so that the appliance is ready once more for deliveringsteam. Such operation can be continued until the tank 144 is emptied orthe appliance is switched off

Whilst the invention has been described in terms of a two specificembodiments, many aspects and features of the invention might be appliedto many different types of appliances, especially other appliances whichgenerate steam such as wallpaper strippers and other hand-held steamgenerating appliances. Features mentioned in connection with theembodiments described in detail above or indeed with any otherembodiments mentioned herein may be applied equally to any otherembodiment and the applicant specifically envisages such combinations offeatures. Any feature of the invention should therefore be considered asindependently applicable and not limited in its application to thisspecific embodiment in which it is mentioned, except where otherwiseindicated.

What is claimed is:

1. A steam generator comprising a water inlet, a boiler, a valve forcontrolling the entry of water into the boiler and a mechanism fordelivering a surge of water to the boiler when the valve is opened. 2.The steam generator as claimed in claim 1 wherein said boiler isarranged such that it is allowed to reach a higher operating temperaturewhen there is no water flow.
 3. The steam generator as claimed in claim1 arranged such that the surge of water comprises a temporarily enhancedflow rate after the valve is opened.
 4. The steam generator as claimedin claim 1 comprising an elastically-charged store upstream of the valvefor storing water.
 5. The steam generator as claimed in claim 4 whereinthe elastically-charged store comprises a reservoir acted upon by aresiliently mounted piston.
 6. The steam generator as claimed in claim 4wherein the elastically-charged store comprises one or more expandablewalls.
 7. The steam generator as claimed in claim 4 wherein theelastically-charged store comprises a bladder.
 8. A hand-held steamgenerating appliance comprising the a steam generator as claimed inclaim
 1. 9. The appliance as claimed in claim 8 wherein the appliance iscordless and comprises an on-board reservoir for supplying water to theboiler during cordless use.
 10. The appliance as claimed in claim 9wherein the capacity of the reservoir is sufficient to provide the waterto generate steam for more than 10, 15, 20 or 30 seconds.
 11. Theappliance as claimed in claim 9 wherein the reservoir is pressurized.12. The appliance as claimed in claim 9 wherein the reservoir has one ormore expandable walls.
 13. The appliance as claimed in claim 9 whereinthe reservoir comprises a bladder.
 14. The appliance as claimed in claim9 wherein the boiler is provided in the mobile/cordless unit.
 15. Theappliance as claimed in claim 9 further comprising a base station andbeing arranged such that the on-board reservoir can be refilled from thebase station.
 16. The appliance as claimed in claim 10 wherein said basestation comprises a base reservoir and a pump arranged to pump waterfrom the base reservoir to the on-board reservoir.
 17. The appliance asclaimed in claim 8 comprising a fixed cord electrical connection, areservoir for supplying water to the boiler, and a pump for pumpingwater from the reservoir.
 18. The appliance as claimed in claim 16wherein said pump is arranged to operate continuously when the applianceis switched on.
 19. The appliance as claimed in claim 16, comprising amechanism to delay operation of the pump until the boiler has reached apredetermined operating temperature.
 20. The steam generator as claimedin claim 1 wherein the boiler comprises a water inlet, an electricheater, a steam outlet and an evaporation space bounded by at least onesurface in thermal contact with the heater, wherein the evaporationspace is configured to present an expanding cross-sectional area in adirection away from the water inlet. 21-30. (canceled)
 31. The steamgenerator appliance as claimed in claim 1 wherein the boiler comprisesan arrangement for collecting steam.
 32. The steam generator applianceas claimed in claim 31 wherein the arrangement for collecting steamcomprises an arrangement for trapping unevaporated droplets of water.33. The steam generator as claimed in claim 1 wherein the boiler isdivided into an evaporation space and a steam collection space by anintermediate member.
 34. The steam generator as claimed in claim 33wherein said intermediate member is heated.
 35. An appliance comprisinga steam generator as claimed in claim 31 and a mechanism for supplyingpressurized water to the water inlet of the boiler.
 36. The appliance asclaimed in claim 9 comprising a base unit and a mobile appliance whereinthe base unit and/or the mobile appliance are configured to preventunwanted disconnection therebetween.
 37. The appliance as claimed inclaim 36 wherein the base unit and mobile appliance comprise anarrangement for preventing separation in a direction substantiallyparallel to the axis of the connection, but which permit removal of theappliance in a direction non-parallel to said axis.
 38. The appliance asclaimed in claim 9 comprising a base unit and a cordless appliance,having mutual cordless connector arrangements for both electrical powerand water, wherein said power and water connections are provided with amutual alignment of mating parts.
 39. The appliance as claimed in claim38 wherein said power and water connections are arranged such that afterphysical contact has been made between one pair of connectors and theyare subsequently brought towards their full alignment axis, physicalcontact is made between the other pair of connectors.
 40. The applianceas claimed in claim 38 wherein said power and water connectors arearranged one higher than the other when the mobile appliance is on thebase unit.
 41. The appliance as claimed in claim 9 comprising a baseunit and a cordless appliance, having mutual cordless connectorarrangements for both electrical power and water, wherein said base unitis provided with a mechanism for reducing the pressure of a pressurisedwater supply while a user is connecting the cordless appliance to thebase unit.
 42. The appliance as claimed in claim 41 wherein the baseunit is arranged to detect when the cordless appliance is brought intoengagement with it.
 43. The appliance as claimed in claim 9 comprising amobile appliance and a base unit and an adaptor for supplying electricalpower to the mobile appliance, said adaptor being operable in a first,corded mode in which it is secured to the appliance to permit electricalpower to be supplied while the appliance is being used; or in a second,cordless mode in which electrical connection between the adaptor and theappliance can be made by placing the appliance on or against theadaptor; and broken by lifting the appliance away from the adaptor. 44.The appliance as claimed in claim 43 wherein said adaptor is designed tobe secured to the base unit or a further base unit.
 45. (canceled) 46.The appliance as claimed in claim 43 wherein the mechanism for supplyingwater from the adaptor to the appliance comprises a valve on either sideof the connection.
 47. The appliance or adaptor as claimed claim 43wherein the adaptor is connected to the base unit.